kern/98034: [geom] dereference of NULL pointer in acd_geom_detach by g_event

[jh at FreeBSD.org]

Synopsis: [geom] dereference of NULL pointer in acd_geom_detach by g_event

State-Changed-From-To: open->closed
State-Changed-By: jh
State-Changed-When: Tue Mar 2 16:27:56 UTC 2010
State-Changed-Why: 
There are multiple problems related to acd(4) detach:

1. acd_modevent() ignored the return value from g_modevent(). This has been
   fixed in r198519 and it may actually prevent the reported panic.

2. acd(4) lacks reference counting and softc locking. (PR kern/125139)

3. There are problems with GEOM class unloading. (PR kern/139847)
   http://docs.freebsd.org/cgi/mid.cgi?20081216210311.GA5229

I am closing this PR because (1) has been fixed and there are duplicate
PRs to cover the other issues.

http://www.freebsd.org/cgi/query-pr.cgi?pr=98034